This invention relates to a relay drive circuit, and more particularly, to a relay drive circuit for an electromagnetic relay.
Electromagnetic relays are typically actuated or picked-up within a specified time duration, commonly termed the "pick-up" or "operate" time of the relays, by the application of a corresponding D.C. voltage across their energizing coil. The pick-up time of the relay decreases with increases in the level of the applied D.C. voltage. After the pick-up time of the relay has expired, the level of the applied D.C. voltage may be decreased and the relay will maintain or hold-in its actuated state.
In electrical systems, such as high-voltage distribution networks, electromagnetic relays are commonly used to interconnect various subsystems within the network. The various subsystems typically have an electronic circuit in their output stage which controls the application of a D.C. voltage for actuating an electromagnetic relay. The electronic circuit is commonly called "a relay drive circuit", and controls the application of the D.C. voltage to the relay typically developed from the power supply source of the subsystem.
The speed of response of the output stage of the subsystem is essentially controlled by the pick-up time of the electromagnetic relay. It is desirable that the subsystem have a relatively fast speed of response; however, electomagnetic relays typically have relatively long pick-up times. For example, the application of a D.C. voltage such as 18 V. D.C. may typically produce a relay pick-up time of 26 milliseconds. The pick-up time of the relay may be reduced by increasing the D.C. voltage level of the power supply source of the subsystem which in turn increases the D.C. voltage level generated by the relay drive circuit. Increasing the D.C. voltage level generated by the relay drive circuit in turn increases the D.C. voltage applied across the energizing coil to thereby increase the speed of response of the subsystem. It is desirable not to supply the large energizing voltage on a steady state basis. However, the overall electronic circuitry within the subsystem, excluding the electromagnetic relay, operates satisfactorily without increased D.C. voltage levels of the power supply. Therefore, it is considered undesirable to impose an overall increase to the subsystem power supply requirements to accommodate the needs of one particular user that being an electromagnetic relay that will be held in with the same D.C. voltage supplied.
Accordingly, it is an object of the present invention to provide a relay drive circuit which enhances the speed of response of the electromagnetic relay without causing any increase to the power supply requirements of the subsystem.
It is another object of the present invention to provide means whereby the D.C. level of energizing the operating signals for the electromagnetic relay controlled by the relay drive circuit may be adaptable to the requirements, such as pick-up and hold-in voltages, of the electromagnetic relay.
These and other objects of the invention will become apparent to those skilled in the art upon consideration of the following description of the invention.